1. Field of the Invention
The present invention is directed to a process for the preparation of aqueous polyurea dispersions by the emulsion polymerization process and to the aqueous polyurea dispersions prepared by this process.
2. Description of the Prior Art
Aqueous polyurethane dispersions are known and are generally prepared by reacting a polyisocyanate with a high molecular weight polyol and low molecular weight chain extender components including components which provide hydrophilicity to the polyurethane. Generally, the polyisocyanate is initially reacted with the high molecular weight polyol to form an NCO prepolymer either in the melt or in the presence of an organic solvent prior to the introduction of water.
In U.S. Pat. No. 3,479,310 the NCO prepolymer is also chain extended to form the linear polyurethane which is then mixed with an organic solvent prior to the addition of water. In U.S. Pat. Nos. 4,066,591 and 4,408,008 the NCO prepolymers are mixed with a solvent, dispersed in water and then chain extended with low molecular weight polyamines.
Accordingly, even though the chain extension step may be conducted in either the organic or the aqueous phase, the reaction between the polyisocyanate and the high molecular weight polyol is not conducted in the presence of water in either process. Further, in both processes organic solvents are necessary to reduce the viscosity of the fully reacted polyurethane or the NCO prepolymer prior to dispersing them in water.
An object of the present invention is to provide a method for preparing aqueous polymer dispersions which does not require the use of organic solvents to reduce the viscosity of fully reacted polyurethanes or NCO prepolymers and which may be conducted using readily available, simple mixing equipment.
Surprisingly, this object may be achieved in accordance with the present invention by reacting polyisocyanates with high molecular weight polyamines by the emulsion polymerization process.